Asphalt has found widespread use as a construction material particularly in the construction of highway pavements, roofing materials, coating building foundations and the like. At ambient temperatures, asphalt is a solid or highly viscous semi-solid liquid. To obtain a low viscosity liquid for easy application, asphalt is heated to reduce the viscosity, dissolved in organic solvents, or emulsified in water using emulsifiers and mechanical shearing. Although asphalt-in-water emulsions are chiefly used for road, parking lot and driveway surfacing, they are also used in the formation and repair of roof surfaces; for damp and waterproofing; for paints, pipe coatings, mastics, anticorrosive coatings; and other applications. For these applications, asphalt-in-water emulsions can be used either alone or in combination with pigments, fillers, fibers, and other inert materials. Depending on their formulation and properties, they can be applied by spray, brush, or squeegee. Such uses, however, may require modifications of the asphalt in order to either facilitate its use or to control other attributes such as drying rates, hardness, water content and dispersion.
There are three categories of asphalt-in-water emulsions determined by the ionic charge of the emulsion. Cationic emulsions contain positively charged particles, whereas anionic emulsions contain negatively charged particles. A non-ionic emulsion is charge neutral. An asphalt emulsion may be further categorized by how quickly it sets up and how long the emulsion is workable. Rapid (fast)-setting emulsions are designed to react with aggregate and quickly revert from the emulsified state to separate states of asphalt and water which runs off and/or evaporates. Fast-setting asphalt emulsions are primarily used for spray applications, such as aggregate (chip) seals, sand seals, surface treatments and asphalt penetration through layers of broken stone. Medium-setting emulsions are designed for mixing with coarse or fine aggregate. These emulsions are more stable than rapid setting emulsions and remain workable for a few minutes. Slow-setting emulsions are designed for maximum mixing stability. The long workability permits thorough mixing with dense-grade aggregates having a high fines content. An anionic, slow-setting emulsion depends solely upon evaporation of the water of the emulsion in order to obtain the asphalt residue coating. That is, the slow-setting emulsion should not coalesce, known as "breaking", upon application of fillers or pigments.
Emulsifying asphalt in water requires the use of an emulsifying agent. Typically, saponification of resins, by alkaline hydrolysis of the resin or by neutralization of fatty acids, yields a detergent or surfactant which may be suitable for use as an asphalt in water emulsifying agent. However, the effectiveness of an emulsifying agent in dispersing asphalt in water varies widely and is unpredictable, in part due to the molecular weight distribution of the original resin or fatty acids. Consequently, not all resins or fatty acids will produce an effective asphalt emulsifier, and there is no known accurate predictor of emulsification effectiveness.
Surfactants are generally classified as anionic, nonionic, or cationic. The surfactant keeps the fine asphalt droplets in stable suspension and controls the breaking time. The surfactant changes the surface tension between the asphalt and water at their interface.
There are many kinds of commercially available surfactants including: 1) olefin sulfonates (such as Bio-Terge AS-90 beads manufactured by Stepan Co., Calsoft AOS-40 manufactured by Pilot Chemical Co., and Witconate AOS manufactured by Witco); 2) lignin sulfonates and their derivatives (such as Lignosite 458 & 823 manufactured by Georgia-Pacific, Temsperse products manufactured by Temfibre, and Indulin SAL manufactured by Westvaco); and 3) alkylaryl sulfonates (such as Calsoft F-90 manufactured by Pilot Chemical Co., and Witconate LX manufactured by Witco).
A commercially available natural acid resin used as an emulsifying agent is Vinsol.RTM. Resin (a natural pine wood resin extracted by Hercules Inc., Wilmington, Del. from Southern Pine tree stumps). Neutralizing Vinsol.RTM. with caustic soda (NaOH) or caustic potash (KOH) forms an anionic water soluble soap used extensively as an anionic emulsifier for asphalt emulsions. Typically, Vinsol.RTM. is added to water at the rate of 6%-10% w/w with water, which in turn is combined with molten asphalt in a shearing mixer, typically a colloid mill. The mixing machine disperses the asphalt in tiny particles throughout the dilute soap Vinsol.RTM. mixture. The final concentration of Vinsol.RTM. in the finished asphalt-in-water emulsion is typically 3%-4% w/w emulsion. The Vinsol.RTM. product, however, is becoming increasingly more expensive as supplies are dwindling, since the Southern Pine tree stumps required for its manufacture are in short supply and less accessible. No suitable replacement for this product has been identified for producing asphalt emulsions.
Whereas a strong emulsifying agent is required to prepare stable anionic slow-setting emulsions of asphalt in water, an even more difficult emulsifying task is to prepare a stable pavement sealer emulsion. Pavement sealers are asphalt-in-water emulsions that contain fillers and additives such as fine aggregate, fibers, clays, and the like. These fillers and additives are used to fill small cracks which occur over time due to weather and wear, and to seal to asphalt pavement. The practice in the industry is to add from about one to three pounds of fine aggregate, fibers, or other filler material per gallon of asphalt-in-water emulsion. The presence of these small particles makes it more difficult to maintain a stable emulsion that does not break down into its water and asphalt components. It typically requires up to twice as much emulsifier to produce a stable asphalt pavement sealer composition as to simply prepare a stable asphalt in water emulsion having no fillers or additives. Consequently there is a need for an emulsifying agent capable of producing a stable filled asphalt-water emulsion without having to have added an additional amount of the emulsifying agent.
Use of tannin or a tannin compound in an asphalt-in-water emulsion is alleged in the published Kao Soap Company Japanese patent document of Ryooichi, et al. (Japanese patent document 63-17960). This Kao Soap document reports on a slow-setting, cationic, asphalt-in-water emulsion. The emulsifying composition includes a surfactant, a tannin or tannic acid compound, calcium chloride and hydrochloric acid to adjust the pH. Quebracho is listed as one of the tannic acid compounds that can be used. The emulsifying composition is combined with heated asphalt in the ratio of 40% w/w emulsifying agent to 60% w/w asphalt. However, the amount of tannic acid or tannic acid-like compound shown by Ryooichi et al. comprises only 0.3%-0.4% w/w of their finished asphalt-in-water emulsion. Attempts to produce a stable anionic asphalt in water emulsion using 0.3% sodium oleate and 0.3% quebracho as cited in the reference were unsuccessful. Doubling the sodium oleate concentration to 0.6% and the quebracho concentration to 0.6% also proved unsuccessful as the combination did not produce a continuous phase asphalt-in-water emulsion, rather producing solid chunks of asphalt in a watery matrix. The cationic process taught by the Kao Japanese patent publication is not applicable to the production of an anionic asphalt-in-water emulsion.
Quebracho is a natural product extracted from the heartwood of the Schinopsis trees that grow in Argentina and Paraguay. Quebracho is a well characterized polyphenolic and is readily extracted from the wood by hot water. Quebracho is currently widely used as a tanning agent. It is also used as a mineral dressing, as a dispersant in drilling muds, and in wood glues. Quebracho is commercially available as a crude hot water extract, either in lump, ground, or spray-dried form, or as a bisulfite treated (refined) spray-dried product that is completely soluble in cold water. Quebracho is also available in a "bleached" form which can be used in applications where the dark color of unbleached quebracho is undesirable.
Other natural vegetable polyphenolic extracts are available including: Chestnut A and Chestnut N, extracted from trees of the genus; Castanea, Sumac-K10, , extracted from the tree Hrhus coriaria; and Wattle Me., extracted from Acacia mollissima (Mimosa) trees. These are currently used commercially in tanning of leather.
Consequently, there is a strong felt need for improved emulsifier compositions capable of emulsifying asphalt, and particularly for stable, slow-setting asphalt-in-water emulsions capable of accepting fillers, additives, pigments and the like.